Filter presses are well known and extensively utilized for separating solids from slurries. Such filter presses employ a plurality of filter plates which are held in contacting relationship between fixed and movable head members while the slurry is pumped into and through the press for collecting the solids in the form of cake between adjacent filter plates. When the press is full, the movable head is backed away from the plates into an open position and the plates are moved into an open position to permit discharge of the cake which is collected between adjacent pairs of plates. To permit movement of the plates into an open position, plate shifting mechanisms are typically provided adjacent opposite sides of the press for permitting automatic or manual control over the plate movement and cake discharge.
Various types of filter plates are utilized in filter presses, depending primarily upon the material to be filtered and the process requirements. For example, one type of plate is a cloth-type chamber plate which includes recessed surfaces on opposite sides of the plate each of which serves to form a filter chamber with an adjacent plate when the plates are clamped together. A cloth filter covers each of these recessed surfaces, and is either mounted on the plate by a gasket or is draped between two adjacent plates. Thus, slurry is pumped into the filter chambers formed between the filter cloths of two adjacent plates, and the liquid from the slurry passes through the filter cloth and is discharged through filtrate ports in the plates. The solids are trapped in the filter chamber and form a cake.
Another type of filter plate which is utilized when process requirements call for production of a dryer filter cake is a diaphragm-type squeeze plate. The construction of this type of plate is similar to the cloth-type chamber plate, but the drainage surfaces on the opposite faces of the plate are flexible diaphragms or membranes which define pressurizing chambers therebehind. A filter cloth covers the outer face of the diaphragm on each side of the plate and typically extends beyond the plate, i.e., the filter cloths are typically draped between the adjacent plates. In this case, slurry is pumped into the filter chambers formed between two neighboring plates and the liquid portion of the slurry passes through the filter cloths and is discharged through filtrate ports in the plates. After the filling cycle is complete and the filter chambers formed between adjacent plates are filled with solids, and before the press is opened, heated air or hot pressurized water is supplied to the chamber located behind each diaphragm, causing the diaphragms to flex outward and exert mechanical pressure on the filter cake. This also effects heating of the filter cake which, in conjunction with a vacuum applied to the discharge side of the filter cloths, causes additional moisture to be removed from the filter cake. An example of this type of arrangement and process is disclosed in U.S. Pat. No. 5,558,773. A similar press and process is also sold by the assignee hereof under the designation "J-VAP".
Diaphragm-type squeeze plates are designed for high-pressure squeeze and must be ported for filtrate discharge. The diaphragm plates are relatively expensive as compared to the cloth-type chamber plates discussed above, for example being typically two to three times as expensive. In this regard, the diaphragm in one conventional construction is integrally joined around the periphery thereof to the ring-like frame of the filter plate, such as by welding. In another conventional construction the diaphragm is a wholly separate plate which overlies and is fixed to the side face of the ring-like frame by fasteners such as screws. Also, the face of the diaphragm which is located behind the filter cloth is typically ribbed in order to define flow paths for liquid discharge behind the filter cloth, and the filter cloth must typically be draped between adjacent plates, which can result in increased liquid leakage from the press. Because of the above, the diaphragms are relatively thick in order to provide structural integrity to the plate. For example, a typical diaphragm may have a thickness of about 0.120 inch between the ribs and about 0.250 inch at the ribs). As such, the thickness of the diaphragm causes a large temperature drop thereacross which impedes heating and thus drying of the filter cake, and this thickness can also impede effective squeezing of the filter cake. These factors thus increase cycle time and decrease the overall operational efficiency of the press.
Accordingly, it is an object of the present invention to provide an improved filter press which overcomes or minimizes the disadvantages of the above-discussed prior art.
One preferred embodiment of the filter press according to the invention includes a filter press having a frame with a pair of generally horizontally elongated and parallel side rails which are disposed in sidewardly spaced relation. Head assemblies are mounted on the frame adjacent opposite ends of the side rails, with a first head assembly being disposed adjacent one end of the side rails for movement horizontally in a lengthwise direction of the side rails forwardly toward and rearwardly away from a second head assembly so as to be respectively positioned in closed and open positions. The second head assembly is stationarily positioned adjacent the other end of the side rails. A plurality of plates are supported on and between the side rails for movement therealong between the two head assemblies. The plates are pushed together into a horizontally extending closed stack and clampingly held between the two head assemblies when the first head assembly is moved toward the second head assembly into the closed position. A plate shifting arrangement effects individual and sequential shifting of the plates from the closed stack along the side rails in the rearward direction toward the first head assembly when in the open position. A first group of plates includes first plates having a frame with a pair of oppositely disposed faces which are recessed inwardly. A liquid impermeable diaphragm or membrane is fixed to the frame and extends across one of the recessed faces to define a first pressure chamber therebetween, and another liquid impermeable membrane is fixed to the frame and extends across the other recessed face to define a second pressure chamber therebetween. A second group of plates includes second plates having a frame with a pair of oppositely disposed faces which are recessed inwardly. A liquid permeable filter member (i.e. cloth or sheet) is fixed to the frame thereof and extends across one of the recessed faces to define a first drainage chamber in communication with a filtrate discharge passage. A second liquid permeable filter member is fixed to the frame and extends across the other recessed face to define a second drainage chamber in communication with a filtrate discharge passage. The first and second plates are disposed in an alternating manner along the side rails in adjacent sealing contact with each other in the closed position of the press so that each two adjacent plates (i.e., the adjacent first and second plates) define a filter chamber therebetween for filtering and collecting solids from a slurry entering the filter chamber. The liquid portion of the slurry penetrates the filter member, enters the drainage chamber and exits the filter press via a filtrate discharge passage, while the solid portion of the slurry remains in the filter chambers. The pressure chamber defined between the liquid impermeable membrane and the recessed face is in fluid communication with a fluid source which expands the membrane towards the opposed adjacent filter member to pressurize the slurry to facilitate liquid-solid separation.
Another preferred embodiment of the filter press according to the invention includes a filter press having a plate arrangement including a plurality of individual plates movable into a closed stack. The plurality of plates includes first plates each including a peripheral edge portion, a central portion recessed inwardly with respect to the peripheral edge portion, a first liquid impermeable membrane extending across one side of the central portion to define a first pressure chamber therebetween, and a second liquid permeable membrane extending across the other side of the central portion to define a second pressure chamber therebetween. The plurality of plates also includes second plates each including a peripheral edge portion, a central portion recessed inwardly with respect to the peripheral edge portion, a first liquid permeable filter member extending across one side of the central portion of the second plate to define a first drainage chamber therebetween, and a second liquid permeable filter member extending across the other side of the central portion of the second plate to define a second drainage chamber therebetween, the second plate being free of membranes. The first and second filter plates are disposed in an alternating manner along the filter press in adjacent sealing contact with one another to define a filter chamber therebetween for filtering and collecting solids from a slurry entering the filter chamber.
Yet another preferred embodiment of the invention includes a plate arrangement including a plurality of individual plates movable into a closed stack. One of the plates includes a peripheral edge portion which surrounds a central portion having two sides which face away from one another and are recessed inwardly with respect to the peripheral edge portion. The peripheral edge portion has a recess disposed therein in communication with a filtrate discharge passage. A liquid impermeable membrane extends across each side of the central portion to define a pressure chamber therebetween, and a liquid permeable filter member extends across each membrane to define a drainage area therebetween. A drainage member is associated with the membrane and is engaged within the recess, and the drainage member has a flow passage disposed therein for providing communication between the drainage area and the recess.
The present invention also relates to a method of effecting liquid-solid separation of a slurry which includes clamping a plurality of plates together into a horizontally extending closed stack such that the plates sealingly contact one another, the closed stack including a plurality of first and second plates disposed in an alternating manner, feeding slurry into the closed stack and into a filter chamber defined between adjacent first and second plates. The liquid portion of the slurry is filtered through filter members disposed on each face of the second plates and discharged into a filtrate vessel, with the solid portion of the slurry forming a filter cake in the filter chambers. Membranes disposed on each face of the first plates are expanded towards the adjacent filter members and against the slurry to facilitate further liquid-solid separation by adding heated fluid to a pressure chamber located behind each membrane.
The present invention also includes a thin flexible diaphragm, for example about 0.023 inch thick. This thin design of the diaphragm provides for more efficient use of the squeeze pressure, and also provides greater heat transfer into the filter cake which raises the temperature thereof to provide more efficient vaporization and vapor draw when vacuum is applied to the liquid discharge passage. The present invention also significantly reduces cycle time, particularly for slurries which tend to fill the press quickly.
The diaphragm plate according to the invention can be constructed from a standard plate by simply machining the plate to accommodate the diaphragm. In this regard, a conventional diaphragm-type squeeze plate is about three to six times as costly as a standard cloth-type filtration plate. However, the diaphragm squeeze plate in accordance with this invention costs approximately the same as the standard cloth-type filtration plate, thereby significantly reducing the overall cost of the press.